Blood-flow tubing

ABSTRACT

An artificial or modified natural blood flow tubing has a helical-flow inducer to induce helical flow in such fashion as to eliminate or reduce turbulence. One inducer is a tubular stent of expansible mesh having a helical vane.

[0001] This invention relates inter alia to artificial or modifiednatural blood-flow tubing, by which is meant artificial vascularprostheses or modified natural grafts or autografts, and tubing in whichblood flows outside the body, e.g. in dialysis or in open heart surgery.Indeed, the invention might well extend to any tubing that carries alaminar flow, and particularly, but by no means exclusively, a pulsatileflow.

[0002] Spiral flow has been observed (Stonebridge P. A. and Brophy C.M., 1991, Spiral laminar flow in arteries? Lancet 338: 1360-61) duringangioscopy, as has the presence of spiral folds on the endoluminalsurface of blood-vessels. The observation, it was said could have beenan artefact of angioscopy, or the phenomenon may occur only in diseasedarteries because of turbulence generated atherosclerosis, or it may bephysiological, the latter having some support from other observations ofrotational flow.

[0003] Indeed, in this seminal article, it is remarked that, ifconfirmed, the existence of spiral rather than laminar blood flow inperipheral arteries would have striking implications for theunderstanding of haemodynamics, arterial wall function, the pathogenesisof atherosclerosis and intimal hyperplasia, and the design of prostheticgraft materials.

[0004] Confirmation came with the publication by Stonebridge and othersof a paper “Spiral laminar flow in vivo” in Clinical Science (1996, 9:17-21) in which, using standard colour flow Döppler techniques, velocityinformation was obtained, from which a rotational element to forwardflow during all or part of the pulse cycle was demonstrated in each ofeleven healthy male volunteers.

[0005] However, even with this confirmation, it was admitted that it hadnot yet been shown whether angioscopic observations of a spiral patternon the endoluminal surface of arteries and spiral flow patterns werereal events or observational artefacts.

[0006] More recent work with magnetic resonance imaging (“MRI”) hasestablished, however, that rotational flow is beneficial at least incertain situations and is presumed, on that account, to be “selectedfor”.

[0007] The prediction, therefore, by Stonebridge and Brophy in the 1991Lancet report is vindicated, though it has only now become apparent justhow to design prosthetic graft materials in order to reproduce, or atleast not to destroy, the physiological rotation, and not at the sametime bring about any disadvantages. It has also become apparent that thefindings are of interest in connection with blood flow tubing other thangrafts, and, indeed, with other tubing as well.

[0008] The invention comprises, in one aspect, tubing, especially, butnot exclusively artificial or modified natural blood flow tubing, havinghelical-flow inducing means adapted to induce helical flow in suchfashion as to eliminate or reduce turbulence.

[0009] The tubing may have internal helical grooving and/or ridging,which may be multi-start grooving and/or ridging. The grooves and ridgesmay be of any cross-sectional shape and size, for example semicircular,square, triangular or sinusoidal—some may be found more effective thanothers in particular circumstances.

[0010] By “helical” as used herein is meant “generally helical”, ratherthan necessarily always mathematically precisely helical.

[0011] Instead of, or in addition to grooving and/or ridging, the tubingmay be of non-circular cross-section, twisted. Synthetic or otherthermoplastic or plastifiable and re-settable material made as astraight, circular or non-circular cross-section tube, may be plastifiedand reset in twisted or corkscrew condition. Non-circular can, ofcourse, include, elliptical, semi-circular, triangular, square or anyother convenient or appropriate shape, including shapes with wavyperipheries which, when twisted, will form grooves and/or ridges.

[0012] The helical formation may have a constant helix angle along atleast a part of its length, or one which reduces or increases over atleast part of its length The grooving and/or ridging, where present, maytaper in the direction of flow or in the opposite direction.

[0013] The helical formation may have a helix angle between 5° and 50°,for example, about 16°. A helical formation having an increasing orreducing helix angle over at least a part of its length may have anangle of 16°, for example, at the start or the finish of the taper, orsomewhere in between. Angles outwith the suggested range may be founduseful, but it is thought the angles above 50° will unduly restrictflow, whereas angles much below 5° will be significantly less effectivethat those in the range. The optimal helix angle will be determined byfactors such as the diameter, longitudinal velocity and rotationalvelocity. In turn, these factors are determined by the particularclinical problem, eg. the type of vessel, the patient's age and the sizeof the native vessel.

[0014] The helical flow inducing means may comprise a bio-compatibleinsert, which may comprise helical vane means, which may, for example,be fashioned like fan or propeller blades or which might be elongatedspiral projections from the inner surface of a cylindrical insert.

[0015] The tubing may have a branched structure in which the flow isfrom a first branch into two second branches in which helical-flowinducing means are provided where the tubing branches so as to eliminateor reduce turbulence downstream from the first branch. The same may beprovided for confluent branches, of course.

[0016] The invention also comprises a method for making blood flowtubing comprising forming the tubing on a mandrel which has helicalgrooving and/or ridging at least over part of its length. The tubing maybe formed, for example, by coagulation casting. In another method,tubing may be formed as cylindrical tubing and a helical formationimparted thereto by wrapping with a thread; the tubing and/or the threadmay comprise thermoplastic material, and the tube heat set to remainstable in the helical formation. In yet other methods, tubing may beformed by woven or knitted graft, or extrusion.

[0017] In yet another method, a non-circular section tube may be formedwith a twisted cross-section either directly on a mandrel itself havinga twisted non-circular cross-section or by making a tube withnon-circular, non-twisted cross-section and then twisting, plastifyingand re-setting the tube in the twisted configuration.

[0018] Tubing made as described may be adapted for use as a vascularprosthesis for implanting into the human or animal body. After-care mayinvolve confirming the helical-flow inducing effect of implanted tubingby measurement of a rotational component of flow, e.g. by MRI, orDöppler ultrasound.

[0019] A method for use in designing tubing for implant in variouslocations in the cardio-vascular system may, according to the invention,involve taking measurements of rotational flow in such locations, as byMRI, in a healthy population in order to determine a typical healthyflow, and designing tubing adapted to produce such flow in suchlocations. Additionally, a method for use in selecting tubing forimplant in various locations of a cardio-vascular system of a specificpatient may involve taking measurements of rotational flow in suchlocations in said patient in order to determine flow, and selectingtubing to produce such flow in such locations (a pre-interventionmethod, which may be facilitated by computer software to aid selection).The design may be by mathematical modelling or by trial and error (exvivo, preferably), with, perhaps, “fine tuning” by after-caremeasurement comparing predicted with actual flows to improve subsequentprostheses.

[0020] Also, according to the invention, intravascular stents, forinsertion e.g. during angioplasty procedures, can have spiral-flowinducing properties.

[0021] The present invention may also be utilised for stent grafts, ie.a combination of stent (providing structure) and graft (internal orexternal material covering).

[0022] A stent, for example, of an expansible mesh material, which isinserted by catheterisation in collapsed form and which becomes expandedon release from the catheter, may have an internal spiral formationafter expansion. Stent which are currently used include those which areself-expanding on release from the catheter, and those which are inducedto expand by mechanical means, eg. using a balloon. The mesh materialmay comprise segments extending helically around the periphery of thestent and the internal spiral formation comprise vane members attachedto such segments—in orther words, the design parameters for the stentmay include both internal and external modification. Styles of stent maybe, for example, mesh (made of configuration of strands or wires givingstructure), expanded sheet (made, cut and modified from sheet) and wirespring.

[0023] Where an insert is used which is accessible, e.g. during vascularimaging, it may be made adjustable, for example its helix angle may beincreased or decreased by extending or contacting a flexible vanearrangement on a rigid support, and this may be done during angioscopywith simultaneous measurement of the rotational component of flowproduced by the insert, whereby to achieve a desired flow.

[0024] Tubing according to the invention may, however, be adapted foruse in or with blood treatment or delivery equipment, such as aheart-lung machine, dialysis equipment or a giving set.

[0025] More generally, the invention comprises tubing havinghelical-flow inducing means adapted to induce helical flow in suchfashion as to eliminate or reduce turbulence or dead flow regions,regardless of the use to which such tubing as adapted.

[0026] Tubing may be utilised to optimise mixing and exhaust of fluid.For example, the tubing design may encourage mixing so as to reducesedimentation, or may beneficially affect the fluid flow pattern (eg.spiral) beyond the outlet of the tubing. The latter effect may beapplied, for example, in tubing such as hoses and firehoses.Optimisation of tubing characteristics may result in a reduction offluid noise at the exhaust or vibration in the tubing.

[0027] The term “tubing” as used here may include all types of conduitwhich transport or contain liquid or gaseous fluid, in both blood andnon-blood fields. Tubing for the blood field may include, but is notrestricted to, graft stems and giving sets.

[0028] Such tubing may have, as with blood flow tubing, internal helicalridging and/or grooving, and other attributes of the blood flow tubingabove referred to. It may particularly be used in plant for deliveringslurries or suspensions of solids in liquids, or, for example, aspipeline for delivering viscous liquids such as oils. It may havehelical flow inducing means at least at interfaces with supply orstorage vessels, and at branches.

[0029] The helical flow inducing means may comprise active flow rotatingmeans, such for example as driven vanes, and such active flow rotatingmeans may be situated at intervals, for example, along a pipeline.

[0030] Embodiments of tubing and methods of making and using the same inaccordance with the invention will now be described with reference tothe accompanying drawings, in which:

[0031]FIG. 1 is a perspective view of a short length of tubing of afirst embodiment suitable for prosthetic implant in a cardio-vascularsystem;

[0032]FIG. 2 is a cross-section of a second embodiment of tubing;

[0033]FIG. 3 is a perspective view of a third embodiment;

[0034]FIG. 4 is a view of the inside of a length of tubing, opened out;

[0035]FIG. 5 in an elevation of a mandrel for use in casting tubingaccording to the invention;

[0036]FIG. 6 is a view of a vaned device in a tube;

[0037]FIG. 7 is a view of a second vaned device in a tube;

[0038]FIG. 8 is a view of a branched tube according to the invention;

[0039]FIG. 9 is a view of a mesh material stent from the side, in itsexpanded condition;

[0040]FIG. 10 is an end-on view of the stent of FIG. 9;

[0041]FIG. 11 is an opened-out view of the stent of FIG. 10;

[0042]FIG. 12 is an end-on view, to a larger scale, of the stent of FIG.11 in its collapsed condition, before release from the catheter;

[0043]FIG. 13 is a view of a pipeline, with active helical-flow inducingmeans; and

[0044]FIG. 14 is a section through the pipeline of FIG. 13.

[0045] The drawings illustrate blood-flow tubing 11 having helical-flowinducing means 12 adapted to induce helical flow in such fashion as toeliminate or reduce turbulence. The tubing may be artificial, forexample woven or knitted synthetic polymer fibre, in which thehelical-flow inducing means may be knitted or woven structure as bythree dimensional knitted or woven formation, or extruded or casttubing, or modified natural, e.g. autograft material with an insert orwith grooving made e.g. by a laser.

[0046] The helical-flow inducing means 12 may comprise grooving 14and/or ridging 15, which may be multi-start grooving and/or ridging asseen in FIGS. 1, 2 and 4. Square-section ridging, as seen in FIG. 1, orgrooving, or semi-circular section ridging and/or grooving, as seen inFIG. 2, can be used, but other cross-sections will serve as well, forexample, triangular.

[0047] However, as seen in FIG. 3, a non-circular section tube 11 canhave a twist, and may also have internal ridging and/or grooving. Atwisted tube may be cast as such on a twisted mandrel or, if, forexample, of thermoplastic material, may be twisted and heat-set in thatstate. Even a circular-section tube, bent into a corkscrew shape, can,if the dimensions are appropriate for the density, velocity andviscosity of the liquid flowing through it, give rise to a circulationin the flow.

[0048] The helical-flow inducing means may extend over the whole lengthof the tubing. It seems, on present knowledge, to be important at leastto provide it where turbulence is likely to occur, for example at theinlet or outlet from the tubing, or in branched tubing as seen in FIG.9, where turbulence can be occasioned in the branch region and can becontrolled by ridging and/or grooving 12 at the inlets to the two minorbranches 11 b where they join the main branch 11 a, and/or in the mainbranch 11 a itself. It may be found desirable to have different ridgingand/or grooving in the two minor branches, where, for example, they runat different angles to the main branch.

[0049] It may be arranged that the ridging and/or grooving 12 has areducing helix angle in the flow direction over at least part of itslength—this is illustrated in FIG. 4, where the grooving 12 is alsotapered so as to extend only over an inlet region L, but the taperingand reducing angle could extend over longer lengths of tubing. Theopposite—helix angle increasing and/or depth of grooving or height ofridging increasing in the flow direction may also be appropriate in somecircumstances.

[0050] The appropriate helix angle, or range of helix angles, whereincreasing or decreasing angles are used, will depend on a number offactors, principally, the dimentions of the tubing, the density andviscosity of the liquid flowing through it, and the velocity of theliquid flow. Generally, it is supposed that angles between 5° and 50°,preferably about 16° will give best results, but angles outside thisrange may also be found to be useful in some circumstances.

[0051]FIG. 5 is an elevation of a mandrel 51 such as may be used in acoagulation casting process to make prosthesis of polyetherurethane orother biocompatible polymer. Grooves 52 are provided on the mandrel 51which then forms a tube with internal ridging.

[0052]FIGS. 6 and 7 illustrate helical vane devices 71 which can beinserted in tubing to cause helical flow. In FIG. 8 the effect can beincreased by a probe 81 as used in angiography. The vanes 82 are on asleeve 83 and sufficiently flexible to be compressed on a rigid support84 by a sleeve 85 of the probe 81 being advanced relative to a core 86,the core 86 engaging the support 84 while the sleeve 85 is advancedagainst the sleeve 83, the sleeve 83 being held in the compressed stateby a ratchet arrangement 87 between support 84 and sleeve 83. Such adevice may be adjusted during angiography while observing the rotationalflow induced, thereby, e.g. by MRI. The adjustment may be effected inany other fashion, e.g. by the application of torque to one end whileholding the other end fixed.

[0053] FIGS. 9 to 12 illustrate an expansible mesh material stent 101which is inserted by catheterisation. Such stents are sometimes made ofa metal with a shape memory and are presented on a catheter in collapsedform, expanding on release from the catheter as they reach bodytemperature, others expand elastically as they are pushed from a captivesurround. In its expanded condition, as shown in FIGS. 9 and 10, thestent 101 comprises a mesh cylinder formed, for example, of welded wires102 with joined segments 103 extending helically around the periphery ofthe stent 101, though some stents are of expanded metal sheet, in whichcase the segments would be integral strips. Attached to some of thesegments 102, on the inside of the stent 101, are vane members 104. In awelded wire construction, these could be plates welded to segments,while in an expanded sheet construction, the vane members 104 could beparts of the sheet, leaving corresponding holes in the mesh. FIG. 11shows an opened-out version of the stent 101, as if cut along agenerator of the cylinder and laid flat, with the inside face uppermost.FIG. 12, which is to a larger scale, shows the stent 101 in collapsedform around a catheter wire 105, without, however, the associatedsurround which contains them for insertion and out from which they arepushed once maneouvered into position.

[0054] Aside from blood flow tubing for implantation, or devices for usein improving circulation, such as bypasses and stents, blood flow tubingis found in various items of medical equipment such as heart-lungmachines, dialysis machines and blood transfusion equipment. Inasmuchas, in such equipment, blood flows much as it does in the body, it couldbe at least as important to fashion such tubing to give the bestpossible flow characteristics, in particular, the avoidance ofthromboses being generated during prolonged use of the equipment, as inheart surgery and dialysis, and the principles set out above in relationto natural and artificial grafts can also be applied to such externalblood flow tubing. Even in giving sets, where flow rate is likely to below, helical flow may well be found to have advantages, especially atthe interfaces between tubing and cannulae and flow regulators.

[0055]FIGS. 13 and 16 illustrate, by way of example, the application ofthe notion of helical flow to an oil pipeline 141. The pipeline 141 isitself made up from pipe sections 142, which may themselves haveinternal helical grooving and/or ridging 143. In addition, active flowrotating means 144 are provided at intervals along the pipeline 141, atjunctions between pipe sections 142. The active flow rotating meanscomprise, as seen in FIG. 13, rotary vanes 145 mounted in connectingrings 146. Depending on circumstances, it may be desirable to drive thevanes by external means, such, for example, as a motor, which can be,for example, solar powered, or it may be preferred to derive power forrotating the vanes from the flow itself, the general idea being torefresh any swirl component that might have attenuated over thepreceding pipe section.

[0056] In addition to pipelines, the idea of helical flow will clearlybe of benefit in plant in which slurries and suspensions of solids inliquids are transported between reactors and storage tanks, forinstance. Examples of such plants are food producing plants, wheresoups, sauces and like products are manufactured.

[0057] It is noted that the mere provision of helical flow inductionwill not necessarily reduce or eliminate turbulence. It will beimportant to select the most appropriate configuration, which may wellbe done by trial and error. It may, of course, be found, especiallywhere sharp bends or corners are encountered in the tubing, that thereis a limit to the stability of rotational flow—it may be desirable, ifpossible, to refashion the tubing to eliminate sharp bends or cornersbefore helical flow will have the effect of inducing or maintainingnon-turbulent flow.

[0058] Designs for the tubing and methods for making the same other thanthose already discussed can of course be envisioned, all falling withinthe scope of the invention.

1. Artificial or modified natural blood flow tubing having helical-flowinducing means adapted to induce helical flow in such fashion as toeliminate or reduce turbulence.
 2. Tubing according to claim 1, havinginternal helical grooving and/or ridging.
 3. Tubing according to claim 1or claim 2, having internal, multi-start grooving and/or ridging. 4.Tubing according to claim 1, of non-circular cross-section, twisted. 5.Tubing according to claim 4, of synthetic or other thermoplastic orplastifiable and re-settable material, being plastified and reset intwisted condition.
 6. Tubing according to any one of claims 1 to 5,having a helical formation having a constant helix angle along at leasta part of its length.
 7. Tubing according to any one of claims 1 to 6,having a helical formation having a reducing or increasing helix angleover at least part of its length.
 8. Tubing according to any one ofclaims 1 to 7, having a helical formation with a helix angle between 5°and 50°.
 9. Tubing according to claim 8, in which the helix angle is16°.
 10. Tubing according to any one of claims 1 to 9, having groovingand/or ridging tapering in the direction of flow and/or in the oppositedirection.
 11. Tubing according to any one of claims 1 to 10, in whichthe helical-flow inducing means comprise a bio-compatible insert. 12.Tubing according to claim 11, in which the insert comprises helical vanemeans, in the form of fan or propeller blades or which compriseelongated spiral projections from the inner surface of a cylindricalinsert.
 13. Blood flow tubing according to any preceding claim, having abranched structure in which the flow is from a first branch into twosecond branches in which helical-flow inducing means are provided wherethe tubing branches so as to eliminate or reduce turbulence upstreamand/or downstream from the first branch.
 14. A method for making bloodflow tubing comprising forming the tubing on a mandrel which has helicalgrooving and/or ridging at least over part of its length.
 15. A methodaccording to claim 14, in which the tubing is formed by coagulationcasting.
 16. A method according to claim 14, in which the tubing isformed as cylindrical tubing, and a helical formation is impartedthereto by wrapping with a thread.
 17. A method according to claim 16,in which the tubing and/or thread comprise thermoplastic material andthe tube is heat set to remain stable in the helical formation.
 18. Amethod for making blood flow tubing comprising forming a non-circularsection tube with a twisted cross-section.
 19. A method according toclaim 18, in which the tube is formed with a non-twisted section, thentwisted and set in the twisted configuration.
 20. Tubing according toany one of claims 1 to 13, or made by a method of any one of claims 14to 19, adapted for use as a vascular prosthesis.
 21. Tubing according toclaim 20, when used as a vascular prosthesis.
 22. A method of treatmentof the human or animal body comprising implanting tubing according toclaim
 20. 23. A method according to claim 22, comprising confirming thehelical-flow inducing effect of implanted tubing by measurement of arotational component of flow after implant.
 24. A method according toclaim 23, in which the measurement is carried out using MRI, or Döpplerultrasound.
 25. A method for use in designing tubing for implant invarious locations of a cardio-vascular system involving takingmeasurements of rotational flow in such locations in a healthypopulation in order to determine a typical flow, and designing tubing toproduce such flow in such locations as by mathematical modelling ortrial and error.
 26. A method for use in selecting tubing for implant invarious locations of a cardio-vascular system of a patient involvingtaking measurements of rotational flow in such locations in said patientin order to determine flow, and selecting tubing to produce such flow insuch locations.
 27. A method according to either of claim 25 or claim26, with fine tuning of the design or selection by after-caremeasurement comparing predicted with actual flows to improve subsequentprostheses.
 28. Tubing according to any one of claims 1 to 13 or made bya method of any one of claims 14-19, adapted for use in blood treatmentor delivery equipment.
 29. Blood treatment or delivery equipmentcomprising tubing according to claim
 28. 30. Equipment according toclaim 29, comprising a heart-lung machine.
 31. Equipment according toclaim 29, comprising dialysis equipment.
 32. Equipment according toclaim 29 comprising a giving set.
 33. An intravascular stent havingspiral-flow inducing properties.
 34. A stent according to claim 33,being an expansible mesh material stent which is inserted bycatherisation in collapsed form and which becomes expanded on releasefrom the catheter, the stent having an internal spiral formation afterexpansion.
 35. A stent according to claim 34, of which the mesh materialcomprises segments extending helically around the periphery of the stentand the internal spiral formation comprises vane members attached tosuch segments.
 36. An insert such as an intravascular stent having ahelical formation to induce spiral flow and being adjustable.
 37. Aninsert according to claim 36, in which a flexible vane arrangement on arigid support has a spiral flow inducer vane with an adjustable helixangle.
 38. Tubing having helical-flow inducing means adapted to inducehelical flow in such fashion as to eliminate or reduce turbulence. 39.Tubing having helical-flow inducing means adapted to induce helical flowin such fashion as to eliminate or reduce dead flow regions.
 40. Tubingaccording to claim 38 or claim 39, having internal helical ridging orgrooving.
 41. Tubing according to any one of claims 38 to 40, used inplant for delivering slurries or suspensions of solids in liquids. 42.Tubing according to any one of claims 38 to 40, used e.g. as pipelinefor delivering viscous liquids such as oils.
 43. Tubing according to anyone of claims 38 to 42, having helical-flow inducing means at least atinterfaces with supply or storage vessels, and at branches.
 44. Tubingaccording to any one of claims 38 to 43, in which the helical-flowinducing means comprise active flow rotating means.
 45. Tubing accordingto claim 44, in which the active flow rotating means comprise drivenvanes.
 46. Tubing according to claim 44 or claim 45, in which activeflow rotating means are situated at intervals along a flowline.